Amid concerns over the growth of al Qaeda-affiliated terrorists, the Department of Homeland Security is advising the Transportation Security Administration to implement "enhanced security measures" at overseas airports with direct flights to the U.S.

DHS Secretary Jeh Johnson announced the measures in a blog post today and said the measures will include "both seen and unseen" security steps.

"We are sharing recent and relevant information with our foreign allies and are consulting the aviation industry," Johnson said. "These communications are an important part of our commitment to providing our security partners with situational awareness about the current environment and protecting the traveling public."

The move comes as military officials indicated foreign terrorists may be using Western passports to evade watch lists. Earlier this week, Air Force Gen. Philip Breedlove said during a Pentagon briefing he was concerned about a possible terrorist attack coming from Syria involving an American or European passport holder.

Breedlove said the concerns mainly center on foreign fighters basing an attack on the U.S. via Europe.

"That is a great concern to me, and it's a great concern to our European partners," he said. "Foreign fighters can return to these nations. They can effect an attack or some sort of problem for that nation and then move quickly across borders into other nations."